[Personalized medicine in oncology: one drug, one biomarker].

Sir Williams Osler, the father of Modern Medicine, recognized more than one century ago, that "If it were not for the great variability among individuals, medicine might as well be a science and not an art". Nevertheless today, in our opinion this paradigm is presently in crisis. Clinical medicine starts to be a science thanks to this variability that is generating a personalized medicine based on the concepts of pharmacogenetic and pharmacogenomic. In the Medical Oncology field this era has begun: today the determination of mutations in several given genes such as Her2, KRAS, EGFR, ALK, and BRAF is translating into a individualized strategy that produces benefits that are clearly superior to present indiscriminate therapeutic decisions. This strategy is more active, more safe and also more efficient.